This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No. 2001-394876 filed Dec. 26, 2001.
1. Field of the Invention
The present invention relates to an earth discharging device for an upward-facing shield machine, and more particularly to an upward-facing shield machine which can securely perform earth pressure control of a work face.
2. Description of the Related Art
FIG. 6 illustrates an earth discharging device for an upward-facing shield machine a previously disclosed by the present inventors. As is shown in the drawing, the upward-facing shield machine a comprises: a vertically-placed tubular shield frame b; a partition wall c which divides the interior of the shield frame b into a work face side and an interior side; and a cutter d which is rotatably mounted on the partition wall c. The shield machine a constructs a tunnel in the vertical direction by causing the cutter d to rotate using a motor e while a jack g is expanded under a reaction force to a pre-installed segment f to cause the shield frame b to rise, whereupon the jack g is caused to contract such that a segment can be provided in a tensioned state in the space between the pre-installed segment f and the jack g manually or using an erector (not shown in the drawing).
The earth and sand that are cut away by the cutter d are taken into a cutter chamber h and discharged by an earth discharging device i. The earth discharging device i comprises: an earth discharging pipe j which is connected to the cutter chamber h and extends downward; an elastic film-type valve k which is provided in the earth discharging pipe i and which opens and closes the interior of the earth discharging pipe i by expanding and contracting diametrically by means of fluid pressure; and an agitator 1 which kneads and fluidizes the excavated earth and sand so that this mixture can be excluded downward more easily by means of gravitational force. The agitator 1 comprises: a rotary shaft n which is disposed in the interior of the earth discharging pipe i and is rotated by a motor m; a collar o which is rotatably fitted over the part the rotary shaft n which faces the elastic film-type valve k; and a kneader blade p which is mounted on the part of the rotary shaft n inside the cutter chamber h.
Meanwhile, the elastic film-type valve k comprises: a tubular elastic film q (rubber film or the like) disposed at a point in the earth discharging pipe i; a tubular casing s which is disposed in a form which covers the outer side of the elastic film q and which forms a pressurizing chamber r with the peripheral surface of the elastic film q; and a supply and discharge port t which is opened in the casing s for supplying and discharging fluid (air, water, etc.) into and out of the pressurizing chamber r. The elastic film-type valve k manages adjustments to the earth pressure on the work face by supplying and discharging fluid into and out of the pressurizing chamber r through the supply and discharge port t such that the elastic film q is caused to expand and contract diametrically to adjust the amount of earth to be discharged.
However, in the aforementioned elastic film-type valve k, when fluid pressure acts equally on the elastic film q, the earth and sand that pass therethrough are at work face pressure (high pressure) at the inlet side and atmospheric pressure (low pressure) at the outlet side. As a result, the elastic film q does not expand equally, as is illustrated by the wavy line in FIG. 6, but is locally pressed inward, as is illustrated by the solid line in the figure, at the outlet side due to the pressure difference between the inlet side and outlet side, thereby becoming tightly pressed against the collar o.
As a result, when the earth and sand at work face pressure inside the cutter chamber h pass through the elastic film-type valve k to drop to the atmospheric pressure side, the earth and sand are locally pressed inward by the pressure difference at the outlet side, whereby the opening adjustment of the elastic film q by means of fluid pressure inside the pressurizing chamber r increases in sensitivity, and earth pressure control at the work face becomes unstable. More specifically, even if the sectional area of the space through which the earth and sand pass is altered in order to control earth pressure at the work face by varying the supply force of fluid to the pressurizing chamber r and varying the amount of expansion of the elastic film q, the elastic film q will be locally pressed inward at the outlet side due to the pressure difference between the upper and lower regions, thereby becoming tightly pressed against the collar o, and as a result, even small alterations in the fluid pressure of the fluid supplied to the pressurizing chamber r will invite repeated blockages and eruptions of the earth and sand, making earth pressure control at the work face unstable.
The pressure difference between the inlet side (work face pressure) and outlet side (atmospheric pressure) grows particularly large when advancing at great depth, and thus the elastic film q is locally pressed inward at the outlet side in accordance with this pressure difference, causing repeated earth and sand blockages and eruptions. Furthermore, in cases where the earth and sand are of a type, such as gravel with a large particle diameter or sandy soil with high frictional resistance, that is difficult to fluidize even using the agitator 1 or by injecting a mud-forming agent or the like, the earth and sand at the narrow opening of the elastic film q, which is locally pressed inward, have a tendency to become blocked such that the frequency of eruptions increases. Consequently, earth pressure control directly above the shield machine a becomes unstable, leading to the possibility of displacement at ground level.
An object of the present invention is to provide an earth discharging device for an upward-facing shield machine which can securely perform work face earth pressure control.
In order to achieve this object, the earth discharging device for an upward-facing shield machine according to the present invention is comprised of: an earth discharging pipe which is disposed in a longitudinal direction in order to discharge downward earth and sand excavated by an upward-advancing, upward-facing shield machine; an elastic film-type valve which is provided in this earth discharging pipe, and which expands and contracts diametrically by means of fluid pressure to open and close the interior of the earth discharging pipe; and a gate mechanism which is provided further toward the outlet side of the earth discharging pipe than the elastic film-type valve, and which adjusts the sectional area of the space inside the earth discharging pipe through which earth and sand pass.
According to the present invention, the earth pressure of the earth and sand can be raised by using the gate mechanism to narrow the sectional area of the space inside the earth discharging pipe at the outlet side of the elastic film-type valve through which earth and sand pass such that the earth and sand at the outlet side of the elastic film-type valve become slightly blocked. Thus, the earth pressure at the outlet side of the elastic film-type valve can be made substantially equal to the earth pressure at the inlet side, whereby a substantially uniform earth pressure can be caused to act upon the entire elastic film-type valve. As a result, the elastic film-type valve expands substantially uniformly, and the earth and sand are pressed inward by the entire elastic film-type valve. Thereby, blockages and eruptions of the earth and sand can be avoided, and earth pressure control can be performed securely regardless of depth or soil type.